1. Field of the Invention
This invention relates to transfer trays that are used by orthodontic treating professionals to bond appliances to the teeth of an orthodontic patient. The invention is also related to methods for making such transfer trays.
2. Description of the Related Art
Orthodontics is the area and specialty of dentistry associated with the supervision, guidance and correction of malpositioned teeth to desired locations in the oral cavity. Orthodontic treatment can improve the patient's facial appearance, especially in instances where the teeth are noticeably crooked or where the upper and lower teeth are out of alignment with each other. Orthodontic treatment can also enhance the function of the teeth by providing better occlusion during mastication.
One common type of orthodontic treatment involves the use of tiny, slotted appliances known as brackets. The brackets are fixed to the patient's teeth and a resilient, generally U-shaped archwire is placed in the slot of each bracket. As the teeth are crooked, the archwire is deflected from its original shape as it is placed in the slot of each bracket. During treatment, the archwire gradually springs back to its original shape and, in so doing, urges the teeth to the desired locations.
The ends of orthodontic archwires are often connected to small appliances known as buccal tubes that are, in turn, secured to the patient's molar teeth. In many instances, a set of brackets, buccal tubes and an archwire is provided for each of the patient's upper and lower dental arches. The combination of brackets, buccal tubes and archwires is commonly referred to as “braces”.
In many types of orthodontic techniques, the precise position of the appliances on the teeth is an important factor in predicting the final teeth positions. One common type of orthodontic technique is known as the “straight-wire” method, introduced by Dr. L. F. Andrews in 1972. In the “straight-wire” method, the set of appliances is configured such that the archwire lies in a horizontal plane at the conclusion of treatment. Consequently, the appliances must be correctly positioned at the beginning of treatment so that the teeth are properly aligned once the archwire straightens and lies in the horizontal plane. If, for example, a bracket is attached to the tooth at a location that is too close to the occlusal or outer tip of the tooth, the orthodontist using a straight-wire technique will likely find that the tooth in its final position is unduly intruded. On the other hand, if the bracket is attached to the tooth at a location closer to the gingiva than is appropriate, it is likely that the final position of the tooth will be more extruded than desired.
One technique for bonding orthodontic appliances to teeth is known as an indirect bonding technique. In the past, known indirect bonding techniques have often used a placement device or transfer apparatus having a shape that matches a configuration of at least a portion of the patient's dental arch. One type of transfer apparatus is called a “transfer tray” or “indirect bonding tray”, and typically has an elongated cavity for simultaneously receiving a number of teeth. A set of appliances such as brackets is releasably connected to the inner surface of the tray at certain, predetermined locations.
During the use of a bonding tray for indirect bonding, an adhesive is typically applied to the base of each appliance by the orthodontist or a staff member. The tray is then placed over the patient's teeth and remains in place until such time as the adhesive hardens. Next, the tray is detached from the teeth as well as from the appliances, with the result that all of the appliances previously connected to the tray are now bonded to respective teeth at their intended, predetermined locations.
Indirect bonding trays are normally custom-made for each patient because the size and orientation of teeth can vary widely from one patient to the next. One method of making indirect bonding trays includes the steps of taking an impression of each of the patient's dental arches and then making a replica plaster or “stone” model from each impression. If desired, the teeth of the model can be marked with a pencil to assist in placing the brackets in ideal positions. Next, the brackets are temporarily bonded to the stone models using a suitable adhesive. An indirect bonding tray is then made by placing matrix material over the model as well as over the brackets on the model. For example, in a thermoforming method, a plastic sheet matrix material may be placed over the model and brackets and then heated in an oven under vacuum. As the plastic sheet material softens and as air in the oven is evacuated, the plastic sheet material assumes a configuration that precisely matches the shape of the replica teeth of the stone model and adjacent brackets. The plastic material is then allowed to cool and harden to form a tray. As an alternative to thermoforming, it is possible to cast a suitable resin, such as silicone, around the teeth of the model and then harden the resin to produce the tray. In this case, a casting vessel is sometimes used to contain the resin prior to hardening.
Once the tray has been formed, it is carefully detached from the stone replica, along with the associated appliances. When the tray is detached, the adhesive used to bond each appliance to the model is typically retained on the base of each appliance. This adhesive pad, also called the custom resin base, conforms closely with the bonding surface on the replica tooth. Finally, the transfer tray is cleaned and trimmed as may be desired to provide a proper fit in the mouth.
While the state of the art with respect to indirect bonding trays has advanced in recent years, there is a continuing need to improve the ease of making and using such bonding trays.